COLLECTION OF SHELLS. 521 



of perna, the largest of which is the p. maxilla- 

 ris, found fossil in Italy and America. The genus 

 malleus derives its name from its form, which 

 is like that of a hammer or the letter T : these 

 shells are remarkable for their size and the small- 

 ness of the cavity in which the animal is lodged. 

 The white species is very scarce ; we have only 

 two specimens from the Molucca islands. The 

 shells belonging to the genus avicula have one 

 side only of the valves very much extended, 

 and when open they appear like two wings 

 borne on a long tail. The largest of the eleven 

 species in the collection is the a. macroptera : 

 of the ligaments of these shells are made the 

 jewels known by the name of peacocks' eyes, a 

 specimen of which is here seen. The species of 

 the genus meleagrina are not very numerous, but 

 they deserve to be noticed, as one of them is the 

 pearl oyster (mytilus margaritiferus , Lin.), which 

 is taken at the depth of many fathoms in the 

 Persian gulph. The pearls are produced by an 

 exudation from the interior of the shell, which 

 is itself wrought into sundry small utensils, ge- 

 nerally known under the name, of mother of 

 pearl. One of these shells is remarkable for the 

 great number of pearls adhering to it. This spe- 

 cies, or one nearly allied to it,, is also found on 

 the coast of Cumana. 



